This invention relates to the field of sintered metal conductors on ceramic substrate materials and bonded conductors such as might be employed in a thick film electrical circuit, for example a surface acoustic wave delay line.
Surface acoustic wave transducers and delay lines find increasing acceptance in modern electronic signal processing in such fields as target detection, voice recognition, mineral exploration, and visual image processing. In each of these applications a need frequently arises to delay the presentation of signals representing one sample of information in order that this sample be compared with a later occuring and related sample of the same information. The surface acoustic wave delay line wherein this delay is achieved by way of the acoustic propagation of radio frequency signals along the surface of a piezoelectrical crystal is a frequent choice of equipment designers for achieving this delay. The ease with which electrical signals can be transduced into physical or mechanical vibrations and then returned to electrical signal form in a piezoelectrical crystal device such as lithium niobate is one reason for this increasing acceptance of surface acoustical wave devices. Other features of these delay lines including realistic time delays, small physical size and mass, and tolerable temperature characteristics, also contribute to this acceptance.
This increasing popularity of surface acoustic wave devices has prompted the United States Air Force to support a program for improving the manufacturing techniques for these devices and to consider innovations which improve the performance and manufactureability of these devices.
Surface acoustic wave devices, thick film structures, and metalization for thick film structures are known in the prior patent art as is shown by the following examples of U.S. patents. The patent of Edwards C. Jelks U.S. Pat. No. 4,194,171 concerns a surface acoustic wave device which is used to perform the mathematical Fourier transform operations and provide a serial output signal from a parallel input signal. The Jelks device employs a silicon substrate that is compatible with the integrated circuit art and attaches a plurality of surface acoustic wave transducers to this substrate rather than employing a piezoelectric material for the entire structure. The Jelks patent comtemplates the use of gold, titanium, aluminum silicon dioxide and zinc oxide materials and discloses a process for fabricating these materials into the discrete Fourier transform device. The Jelks patent is an example of the devices currently employed in signal processing circuitry, and includes a discussion of the related applications and fabrication technology.
The patent of Shusuke Ono U.S. Pat. No. 4,236,095 concerns a surface wave device which employs A-alumina as an acoustic wave transmitting substrate. The Ono substrate is coupled to a pair of piezoelectric transducers fabricated from crystalline zinc oxide. The Ono patent is especially concerned with providing good acoustic coupling between a transducer and the surface acoustic wave substrate and with the selection of materials having good surface acoustic wave properties.
The patent of William R. Scott et al. U.S. Pat. No. 4,339,683 discloses an electrical connection apparatus suitable for use on a piezoelectric material. The Scott invention uses a gold layer as an intermediary for making a low temperature solder connection. The piezoelectric material of choice in the Scott patent is polyvinylidene fluoride, a material presenting unusual electrode and lead attachment problems. The Scott patent is primarily concerned with the fabrication of a satisfactory electrode on polyvinylidene fluoride transducer members.